Certain pectins, e.g. pectin from sugar beets and pectin from spinach, as well as hemicellulosic material from certain cereals, e.g. from wheat and maize, are substituted to some extent with substituents derived from certain carboxylic acids (normally substituted cinnamic acids) containing phenolic hydroxy groups. Substances of this type are, for convenience and brevity, often referred to in the following simply as "phenolic polysaccharides".
A number of naturally occurring phenolic polysaccharides of the above-mentioned type are readily available relatively cheaply and are of proven physiological safety with regard to ingestion by, and contact with, humans and animals. Such phenolic polysaccharides have numerous applications relating to their ability to undergo gelling or viscosity increase under certain conditions. Areas of application of the resulting gelled or viscous products include, but are by no means limited to, the following:
Foodstuff applications: as a thickening and/or stabilising agent in sauces, gravy, desserts, toppings, ice cream and the like; as a setting agent in marmelades, jams, gellies and the like; as a viscosity-regulating agent in flavouring extracts and the like.
Medical/medicinal applications: as a material for drug encapsulation; as a slow release vehicle for drug delivery (e.g. oral, anal or vaginal); as a material for a wound or burn dressing.
Agricultural/horticultural applications: as a slow release vehicle for pesticide delivery (i.e. as a biocontainer); as a plant culture medium.
Oxidative cross-linking of phenolic polysaccharides of plant origin (with resultant gelling) is described in, e.g., FR 2 545 101 and WO 93/10158, and by J. -F. Thibault et al. in The Chemistry and Technology of Pectin, Academic Press 1991, Chapter 7, pp. 119-133.
The cross-linking of phenolic polysaccharides may be achieved by purely chemical modification using a powerful oxidant such as, e.g, persulfate [as described in J. -F. Thibault et al. (vide supra) in connection with the gelling of beet pectins].
With respect to enzyme-catalyzed processes, J. -F. Thibault et al. (vide supra) also describe the gelling of beet pectins using a combination of a peroxidase and hydrogen peroxide. Similarly, WO 93/10158 describes gelling of aqueous hemicellulosic material containing phenolic substituents (e.g. substituents derived from "ferulic acid" (i.e. 4-hydroxy-3-methoxycinnamic acid; it does not appear to have been established clearly whether "ferulic acid" embraces cis or trans isomeric forms, or both) using an oxidizing system comprising a peroxide (such as hydrogen peroxide) and an "oxygenase" (preferably a peroxidase).
FR 2 545 101 A1 describes a process for modification (including gelling) of beet pectin involving the use of "an oxidizing system comprising at least an oxidizing agent and an enzyme for which the oxidizing agent in question is a substrate". However, the only types of oxidizing agent and enzyme which are specified and/or for which working examples are given are hydrogen peroxide and peroxidases, respectively.
The documents outlined briefly above describe, inter alia, the use of the resulting modified/gelled materials for medical/medicinal purposes, in cosmetics and/or in foodstuffs. However, neither peroxide treatment nor chemical modification of substances intended for ingestion (e.g. substances for use in foodstuffs) or for uses which may result in more or less prolonged contact with, or close proximity to, skin or mucous membranes are desirable, and such treatments are in fact not permitted in many countries. As will be apparent from the above discussion, there seems to be a lack of real awareness of the possibility of avoiding such undesirable treatments, and it is an object of the present invention to provide an alternative to the existing methods.